There have been conventionally proposed techniques for extracting a specific wavelength range of light from sunlight. For example, an ultraviolet sensor is capable of receiving ultraviolet light and outputting photoelectric current. In addition, a semiconductor light receiving element is capable of detecting the intensity of only visible light among received light.
However, such conventional techniques could not precisely extract desired light due to a sensitivity deviation which may be caused by ringing of spectral sensitivity of a filter transmittance.
For example, an UV cut filter and two photodiodes may be used to extract an UV wavelength range R1 of the light as shown in FIG. 21B from sunlight as shown in FIG. 21A. In this case, in order to extract the UV wavelength range R1 of the light, there is a need to subtract the “output from a photodiode A1 provided with no filter” as shown in FIG. 22B from the “output from a photodiode A2 provided with a filter” as shown in FIG. 22A. However, for example, when the UV cut filter is attached to the photodiode A2, ringing in a spectral sensitivity of a filter transmittance occurs while light other than ultraviolet light can be transmitted, as shown in FIG. 23A. The ringing occurs due to an interference between reflected waves at a surface and a lower portion of the filter, as shown in FIG. 23B. If ringing in the output of the photodiode A2 occurs as shown in FIG. 22B, the output of the photodiode A1−output of the photodiode A2 will include some remaining light in a wavelength range other than the UV wavelength range R1, which may result in a sensitivity deviation, as shown in FIG. 22C. Thus, the conventional techniques have a problem in that the sensitivity deviation increased as the manufacture tolerance of filters has a direct effect when the output of the photodiode A2 is subtracted from the output of the photodiode A1 (i.e., output of a first photodiode A1−output of a third photodiode A2).